1. Field of the Invention
The present invention relates to a semiconductor device and its manufacturing method, and, more particularly, to a semiconductor device subjected to the application of so-called multi-chip module techniques, in which a plurality of semiconductor chips are incorporated as one electronic component, and its manufacturing method.
2. Description of the Related Art
To meet the demands of miniaturized lightweight, and low-energy consumption electric and electrical products, together with the high integration technology of semiconductor chips, packaging techniques to mount these semiconductor chips in high density have also been developed. Among such packaging techniques, multi-chip module (hereinafter referred to as “MCM”) techniques, in which a plurality of semiconductor chips are mounted as one electrode component on the same supporting substrate and pre-packaged, have been developed to bring about even higher density packaging, in addition to multi-layer wiring supporting substrates, bear-chip packaging, and the like. By building more than two semiconductor chips on a single substrate, the MCM techniques practically realize multi-functionality.
Referring to FIG. 13, this is a plan view of an example of a semiconductor device using such an MCM technique. A semiconductor device illustrated herein is constituted with two semiconductor chips 102 and 103 having divergent functions mounted on a supporting substrate 101. On each of the semiconductor chips 102 and 103, there are installed internal circuits 102a and 103a in which respective functional chips are formed; external connection circuits (so-called interface circuits) 102b and 103b drawn from these internal circuits 102a and 103a; and electrode pads 102c and 103c connected to the external connection circuits 102b and 103b. Moreover, the semiconductor chips 102 and 103 are connected to each other with wiring 104 set up between the electrode pads 102c and 103c. 
A semiconductor device of the MCM type mentioned above, in comparison with a semiconductor device of the LSI system type having a plurality of semiconductor chips built in, realizes the same degree of high functionality while simplifying design and wafer processes, hence, it is advantageous in terms of yield, production cost, and shortened TAT (Turn Around Time).
In each semiconductor device of the MCM type mentioned above, FIG. 13 is presented as an example to describe that the connection between the semiconductor chip 102 and the semiconductor chip 103 is established by way of the external connection circuits 102b and 103b. These external connection circuits 102b and 103b are necessary for testing the internal circuits 102a and 103a regarding respective semiconductor chips 102 and 103. For example, each of the external connection circuits comprises an I/O interface circuit, a power circuit, an electrostatic protective circuit, and the like.
Since each of these circuits requires a very substantial quantity of current, an increase in power consumption of the entire semiconductor device is caused. Such increase in power consumption leads to increasing calorific power in the semiconductor device, which in turn leads to deterioration of its reliability.
Further, connecting between the semiconductor chips 2 and 3 via the I/O circuit makes high-speed operation difficult.
In view of these problems, the present invention meets a need to provide a semiconductor device of the MCM type capable of high-speed operation and low power consumption and its manufacturing method.